You can consume Crystal and raise your Rank when you reach certain amount of enemy defeats, Obelisk/Core destruction, or World VS playing time.
By raising your Rank, within World VS, you will be able to gain more Crystals by defeating an enemy, and get access to the new World VS Shop.
If you reach certain Rank, your appearance in the mini-map will change.
On top of that, if you are in the victorious Force, you will be able to receive "War God Medal", amount according to the Rank in the final day!
"War God Medal" is an item that is used to purchase Pack filled with gorgeous items, after the end of World VS.